1. Field of the Invention
This invention relates to a process for the simultaneous manufacture of epsilon-caprolactones and carboxylic acids, and more particularly, to the co-oxidation of cyclohexanones and aldehydes to epsilon-caprolactones and carboxylic acids, respectively.
2. Description of the Prior Art
Epsilon-caprolactone is a commercially significant intermediate for formation of a polyester for urethane-polymer manufacture. U.S. Pat. No. 3,025,306 to Guest, issued Mar. 13, 1962, discloses the conversion of cyclohexanones to epsilon-caprolactones by the co-oxidation of the cyclohexanones and aldehydes in the presence of a catalyst such as cobalt, manganese, platinum, palladium, vanadium, ruthenium, zirconium, aluminum, antimony, beryllium and copper. However, this process is characterized by relatively high yields of unwanted by-products such as adipic acid and a relatively low efficiency of the use of the aldehydes, that is, an increased formation of carboxylic acids.
U.S. Pat. No. 3,483,222 to Sennewald, issued Dec. 9, 1969, discloses the preparation of an epsilon-caprolactone by reacting a cyclohexanone with oxygen in the presence of an aldehyde and a soluble iron compound. This process suffers from a relatively low catalyst activity and is not satisfactory for the production of an epsilon-caprolactone from a cyclohexanone.
British Pat. No. 1,009,773 discloses a process for the production of epsilon-caprolactones and carboxylic acids by the co-oxidation of a cyclohexanone together with an aldehyde in the liquid phase with molecular oxygen at a temperature in the range of 50.degree. C to 150.degree. C, the reaction being carried out in the absence of any deliberately provided metallic compounds possessing catalytic activity under the reaction conditions. Also, this reference teaches that when metal compounds are present in low concentrations in the starting materials or when they are introduced upon contact of the reactants and/or the reaction products with the reaction vessel, it is advantageous for the process to be carried out in the presence of sequestering agents such as amino carboxylic acids (EDTA), nitrilo triacetic acids, 1, 2-diamino cyclohexane tetra-acetic acid, hydroxyethyl derivatives of amino triacetic acid, nitrogen-containing heterocyclic compounds (2,2'-bipyridyl, dipicolinic acid), organic phosphates and phosphites, polyphosphates, hydroxy carboxylic acids, 1, 3-diketones, polyamines and Schiff's bases.
Thus, the process of this patent is characterized by the absence of any deliberately provided metallic compounds possessing catalytic activity and the addition of a sequestering agent. However, the aforementioned process poses disadvantages for commercial operation because the low reaction rates of this process, arising from the absence of a catalyst, require higher reaction temperatures which result in lower selectivities of the product epsilon-caprolactones. Moreover, it is to be noted that the preparation of cyclohexanone and butyraldehyde in the presence of metal ions (Mn, Fe, Co, Ni, Zn) and a sequestering agent (2,2'-bipyridyl) is disclosed in Example 11 (Run No. 8) of this patent. One disadvantage of this process is the low selectivity caused by the high reaction temperature and the presence of the harmful heavy metallic ions which catalyze overoxidation reactions. Still a further disadvantage is the use of a large amount of 2,2'-bipyridyl, which lowers the selectivity and makes the process expensive. Furthermore, it is to be noted that there is no indication in this patent that the combination of an iron compound and 2,2'-bipyridyl is a catalyst for the co-oxidation of a cyclohexanone and an aldehyde.
There is a need, therefore, for a more efficient, selective and inexpensive process for the production of epsilon-caprolactones from cyclohexanones.